Bandpass Filter Specs

Note: the following specifications are applicable to BOTH bandpass filters and delay lines.

  1. Do not specify and tolerance the PassBand center frequency and bandwidth, instead define without tolerance the center Fo and width B of the PassBand in which p-p amplitude and phase ripple are specified.
  2. Specify the minimum insertion loss in the defined PassBand.
  3. PassBand ripple and return loss may need to be relaxed for realisability at the PassBand edges.
  4. Do not specify bandwidths unless truly necessary, and then only a max or min, not both. Do not specify amplitude or phase ripple in the transition bands. These specs can drive yields down and costs up. Transition band shape is not easily designed. If max noise band width is important then specify it.
  5. Do not specify and tolerance a rejection bandwidth, instead define without tolerance the StopBand in which rejection levels are then specified, if necessary with multiple segments. Do not extend the StopBand below Fo/2 or above 2Fo unless truly necessary. Delay line StopBands are usually not specified.
  6. Test is performed in a 50 ohm system with return loss usually unspecified. If necessary, specify the minimum return loss either at F0 or in B. Return loss will always degrade near the PassBand edges. A 1dB increase in input and output return loss will cause a 1dB increase in insertion loss. Do not specify return loss outside the PassBand, assume it’s zero.
  7. A polynomial is least mean squared fit to the un-wound measured phase vs freq. Phase is then shown as the deviation from that polynomial, and insertion delay is the derivative of that polynomial at Fo.
  8. Do not specify group delay ripple, it is highly dependent on insertion delay and far-out time spurious, instead specify p-p phase deviation ripple in B.
  9. Time domain spurious, eg feedthru and triple-transit, may be specified.
  10. Specify the operating temperature range with care, an excess can drive yields down and costs up.
  11. Non-operating temperature range can be -55C to 125C.
  12. When appropriate, key system level performance parameters may be specified. They can be verified by computer simulation based on measured frequency data. Simulation software has been prepared for: time response for any input signal, pulse widths and sidelobes, inter-symbol interference (ISI), signal to noise ratio loss, bit error rate (BER), TV K-factor, and many others.